1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).
Here, the side of the positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Patent Application Publication Nos. 2011/0058272 A1 and 2011/0170381 A1, and U.S. Pat. No. 8,614,932 B1 each disclose a technology in which the surface of the core of the waveguide and the surface of the plasmon generator are arranged to face each other with a gap therebetween, so that evanescent light that occurs from the surface of the core based on the light propagating through the core is used to excite surface plasmons on the plasmon generator to generate near-field light based on the excited surface plasmons.
A thermally-assisted magnetic recording head that employs a plasmon generator as a source of generation of near-field light is configured so that the write head unit includes a coil, a main pole and the plasmon generator. The coil is configured to produce a magnetic field corresponding to data to be written on a recording medium. The main pole has an end face located in the medium facing surface. The main pole is configured to allow a magnetic flux corresponding to the magnetic field produced by the coil to pass, and configured to produce a write magnetic field from the aforementioned end face. The plasmon generator includes a near-field light generating part located in the medium facing surface. It is required of the thermally-assisted magnetic recording head that the end face of the main pole and the near-field light generating part of the plasmon generator be located in close proximity to each other.
Thermally-assisted magnetic recording heads are being often used in high-end, large-capacity magnetic disk drives typified by those for cloud computing business. Highly reliable thermally-assisted magnetic recording heads applicable to high-end, large-capacity magnetic disk drives are thus in demand.
However, thermally-assisted magnetic recording heads suffer from the problem that heat generated by the plasmon generator causes corrosion of the main pole, and thereby reduces the life of the thermally-assisted magnetic recording head. Corrosion of the main pole occurs as follows. The heat generated by the plasmon generator is transferred to the main pole through the inside of the head and/or through the recording medium. As a result, the main pole gets hot. The hot main pole chemically reacts with atmospheric oxygen and moisture, and thereby suffers corrosion.
One of solutions to the aforementioned problem is to provide a heat sink around the main pole. U.S. Patent Application Publication No. 2011/0170381 A1 discloses a thermally-assisted magnetic recording head with two metal layers of a nonmagnetic metal disposed on opposite sides of the main pole in the track width direction. This thermally-assisted magnetic recording head will hereinafter be referred to as the conventional head.
In order to improve the heat dissipation performance of the two metal layers in the conventional head, it is necessary to increase the volume of the two metal layers and the areas of respective end faces of the two metal layers exposed in the medium facing surface. However, the conventional head has encountered the following first and second problems.
The first problem is that because the two metal layers formed of a different material from that of the main pole extend broadly around the main pole, large stresses may be generated on the two metal layers to cause them to peel away and/or cause damage to the plasmon generator located near the two metal layers.
The second problem is increased cost of the head. Suitable materials for the two metal layers are nonmagnetic metals having high thermal conductivity. Examples of the nonmagnetic metals having high thermal conductivity include a noble metal such as Au or Ag. However, the use of such a noble metal to form the two metal layers of large volume increases the cost of the head.